For example, in a power supply circuit that is provided to a power supply apparatus for an electronic device such as AC-DC converter that converts a voltage from a commercial alternating current voltage to a direct current voltage, an input part alternating current (hereinafter, also referred to as AC) power is provided with a variety of filter circuits (line filters). The filter circuit is provided so as to suppress a noise from being leaked or introduced through a wiring. The filter circuit may include a filter capacitor that is arranged between an L pole and an N pole of AC lines connected to an AC power supply (across-the-line capacitor). The filter capacitor has an effect of suppressing noises of the AC lines.
In the power supply circuit having the filter capacitor, when an input path of the AC is interrupted at a forward end position (a portion close to an output terminal side of the AC power supply) more than the filter capacitor, charges corresponding to a capacity of the filter capacitor remain in the filter capacitor, i.e., between both poles of the AC. For example, when an AC plug of the electronic device and the like is pulled out from a plug socket and thus interrupts the input path of the AC, a remaining voltage accompanied by the remaining charges occurs between both electrodes of the AC plug.
In order to suppress the user from getting an electric shock, it is necessary to remove the remaining charges. Regarding the remaining charges, a variety of reference values is defined in the standards and the like. For example, IEC60065-9.1.6 defines a remaining voltage value after 2 seconds from the interruption of the AC. Also, IEC60950-2.1.1.7 defines a time constant (1 second or below) of remaining voltage decay.
By using a below-described method, the remaining charges between both poles of the AC are removed to decay the remaining voltage, the power supply circuit to satisfy the reference values and to be suitable for the standards and the like is provided. That is, regarding the method of removing the remaining charges, a so-called discharge resistance method, an IC method, a circuit method and the like are adopted.
FIG. 9 is a circuit diagram illustrating an example of a power supply circuit adopting the discharge resistance method.
FIG. 9 shows a power supply circuit 801, in which the discharge resistance method is adopted. The circuit is an AC-DC converter having an AC power supply VAC, a resistance R81, capacitors C81, C82 and a coil L81. Both ends of the filter capacitor C81 are respectively connected to two output terminals (L pole, N pole) of the AC power supply VAC. The resistance R81 is connected in parallel with the filter capacitor C81 at a part closer to the output terminals of the AC power supply VAC than the filter capacitor C81. When interrupting the AC, charges of the filter capacitor C81 flow to the resistance R81. Accordingly, when interrupting the AC, the charges of the filter capacitor C81 are removed. The discharge resistance method has merits in that it is realized at low cost and the power supply circuit 801 has a simple configuration.
In the meantime, according to the IC method, a discharge circuit to discharge the remaining charges is integrated and provided to a power supply circuit. In the IC method, since it is possible to make the discharge circuit small, it is possible to miniaturize the power supply circuit or an apparatus having the same mounted thereto.
The circuit method is described as follows.
That is, JP-A-2001-095261 and JP-A-2010-004613 disclose technologies about configurations or controls of suppressing current from flowing between the L pole and the N pole of the AC lines through the discharge resistance when AC is input, i.e., when the power supply circuit operates. Both JP-A-2001-095261 and JP-A-2010-004613 discloses a circuit configuration, in which a discharge path of the remaining charges when interrupting the input path of the AC is provided between the different poles (L pole and N pole) of the AC lines.
JP-A-2006-204028 discloses a direct current power supply apparatus, in which a path at a low voltage side after rectification is configured as the path of discharging the remaining charges when interrupting the AC input path.